Both increased and decreased rates of fetal growth are associated with adverse infant and maternal health outcomes. While the causes and health risks of restricted fetal growth have been studied extensively, the etiology of excess fetal growth has received less attention. Fetal overgrowth is associated with increased risk of birth trauma and cesarean delivery. Furthermore, excess fetal growth appears to predispose infants towards developing into overweight children. Thus, examining factors that could modify fetal overgrowth may uncover new pathways for preventing childhood overweight status. Our research team has found that maternal physical activity during pregnancy may control fetal overgrowth. However, the independent effects of pre-pregnancy exercise training status, pregnancy physical activity habits, and maternal body size on fetal growth are not clearly delineated. The proposed study seeks to evaluate the effects of pre-pregnancy and trimester-specific physical activity on fetal growth and toddler body size while controlling for maternal body size and pregnancy-related weight gain. We will investigate these relationships using a cohort of 298 women who recently participated in a study that recorded their physical activity at the time of their first prenatal care visits. Women will be contacted ~1.5-2.5 years after their pregnancies. Pre-pregnancy and trimester specific physical activity histories will be recorded and validated using previously collected data. Infant birth weight and other pertinent perinatal information will be gathered from birth records and medical records with the mother's consent. Toddler height and weight at ~18-28 months old will be reported by the mother. We hypothesize that pregnancy physical activity will help control fetal overgrowth and will alter relationships between fetal growth and toddler body size. If proven true, pregnancy physical activity may decrease risk of birth trauma associated with having a large infant and may also provide a new strategy for addressing the major public health concern of childhood overweight. This project has the potential to help improve the health of women, infants, and children and addresses the Centers for Disease Control and Prevention Health Impact Goal of Healthy People in Every Stage of Life to "Start Strong" by promoting healthy pregnancy and birth outcomes. Identifying the role of pregnancy physical activity participation on fetal growth could inform future research concerning physical activity recommendations for child-bearing women and improve maternal health. Gaining insight into potentially modifiable determinants of fetal growth could also have downstream effects on infant and child health, since birth size has been related to several future health conditions, including childhood overweight status. [unreadable] [unreadable] [unreadable]